   (not (seq? a)))
 
 (defn null? [a]
-  (or (= '() a)
+  (or (= [] a)
       (nil? a)))
 
 (defn lat? [l]

; end of LISPer, bonus practice
(defn subst2 [n o1 o2 lat]
  (cond
    (null? lat) '()
    (or (= (first lat) o1)
        (= (first lat) o2)) (cons n (rest lat))
    :else (cons (first lat)


(defn multisubst [n o lat]
  (cond
    (null? lat) []
    (= (first lat) o) (cons n
                            (multisubst n o (rest lat)))
    :else (cons (first lat)
